Add pitch bend research data.

Subversion-branch: /research
Subversion-revision: 1656

opl/pitchbend/README

@@ -0,0 +1,17 @@
+
+Constructed MIDI to test pitch bend effects.
+
+Findings:
+
+ * Doom ignores the least significant bit of pitch bend events
+
+ * The "range" of the pitch bend extends over the nearest two notes,
+   ie. when bent down to the minimum, notes sound two semitones lower
+   than normal, when bent up to maximum, notes sound two semitones
+   higher than normal.
+
+ * The full pitch table is in doom2.exe starting at 0x0008864c
+
+ * When bent up at the highest note, the MIDI code overflows the pitch
+   table slightly and uses the next value in memory (0x36c)
+

opl/pitchbend/freqs-to-csv

@@ -0,0 +1,26 @@
+#!/usr/bin/env ruby
+
+require "scanf"
+
+index = 0
+
+$stdin.each_line do |s|
+
+	if s !~ /Key on.*octave (\d+), freq 0x([0-9a-f]+)/
+		next
+	end
+
+	octave = $1.to_i
+	freq = $2.scanf("%x")
+
+	if index > 0
+		puts "#{index},#{octave},#{freq}"
+	end
+
+	index += 1
+
+	if index >= 512
+		break
+	end
+end
+

opl/pitchbend/freqs2.csv

@@ -0,0 +1,511 @@
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opl/pitchbend/gen-sequence

@@ -0,0 +1,51 @@
+#!/usr/bin/env ruby
+
+def note_on(delay, channel, note, volume)
+    # note on
+    putc delay
+    putc 0x90 + channel
+    putc note
+    putc volume
+end
+
+def note_off(delay, channel, note)
+    # note on
+    putc delay
+    putc 0x90 + channel
+    putc note
+    putc 0x00
+end
+
+def pitch_bend(delay, channel, bend)
+    putc delay
+    putc 0xe0 + channel
+    putc (bend & 0x7f)
+    putc ((bend >> 7) & 0x7f)
+end
+
+def end_of_track
+
+    # end of track
+
+    putc 0x00
+    putc 0xff
+    putc 0x2f
+    putc 0x00
+end
+
+# Play the same note pitch bent at various values.
+# This doesn't check the full 0...16384 range but should
+# be enough
+
+for i in 0...512
+    pitch_bend(0x3, 8, (i * 16384) / 512)
+
+    # Turn on a note on channel 8:
+
+    note_on(0x3, 8, 30, 0x40 + (i % 32))
+
+    note_off(0xa, 8, 30)
+end
+
+end_of_track
+